Resource Reservation Protocol (RSVP) is a protocol, i.e., a transport layer protocol as defined in Request for Comments (RFC) 2205 which may be found at http://www.rfc-editor.org/rfc/rfc2205.txt, designed to allow an application to reserve resources across a network for a given data flow. A data flow is typically constrained in scope to a 5-tuple identification that includes a source address, a destination address, a source port, a destination port, and a transport protocol.
Within the context of realtime video and video communications, RSVP reservations are typically established pre-ring, i.e., before a phone associated with a potential answering agent rings. In other words, a call request that specifically offers or requires in call signaling messages establishing a reservation for a call generally causes a reservation to be established, e.g., by a call center server, prior to an agent answering the call, and/or prior to media being sent to the agent. When multiple agents may be eligible to answer a call, reservations between a caller and each of the multiple agents are attempted prior to any of the agents answering the call. For example, the phones of the agents generally do not ring until after reservations associated with a call are established. When reservations are established between a caller and each call agent that may potentially answer a call, bandwidth which may be used for other calls is unnecessarily reserved.
RFC 3312, entitled “Integration of Resource Management and Session Integration Protocol (SIP)” (hereinafter, “RFC 3312”), describes a method that allows for reservation establishment. According to RFC 3312, each device that may be called receives a SIP offer from a calling device, i.e., a caller, and responds to the calling device with another SIP message, e.g., an answer. The answer includes an Internet Protocol (IP) address, port information, and status information relating to a desired reservation. SIP signaling becomes relatively complicated when multiple devices that may be called are involved. Each device that may be called exchanges signaling messages before a call may be answered by one device, and each of the signaling message are processed, in turn, by elements in a signaling path as well as by a calling device.